1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a horizontal electric field type liquid crystal display device and a driving method thereof that improve a picture quality and reduce power consumption.
2. Discussion of the Related Art
A liquid crystal display (LCD) device controls light transmissivity of liquid crystal molecules using an electric field to display images. A liquid crystal display device is generally divided into a vertical electric field type and a horizontal electric field type in accordance with the direction of the electric field that controls the liquid crystal molecules.
A vertical electric field type liquid crystal display device has a common electrode formed on an upper substrate and a pixel electrode formed on a lower substrate arranged opposite to each other to generate a vertical electric field therebetween and to drive liquid crystal molecules of a twisted nematic TN mode using the vertical electric field. The vertical electric field type liquid crystal display device has an advantage of a high aperture ratio, but a disadvantage of a narrow viewing angle of about 90°.
In contrast, a horizontal electric field type liquid crystal display device has a common electrode and a pixel electrode arranged in parallel on a lower substrate to generate a horizontal vertical electric field therebetween and to drive liquid crystal molecules of an in-plane switch mode using the horizontal electric field. The horizontal electric field type liquid crystal display device has an advantage of a wide viewing angle of about 160°.
FIG. 1 is a schematic block diagram illustrating a horizontal electric field type liquid crystal display device according to the related art. In FIG. 1, a horizontal electric field type liquid crystal display device includes a liquid crystal display panel 10, a data driver 2 for driving data lines DL1 . . . DLm of the liquid crystal display panel 10, a gate driver 4 for driving gate lines GL1 . . . GLn of the liquid crystal display panel 10, a timing controller 6 for controlling the gate driver 4 and the data driver 2, and a common voltage generator 8 for supplying a reference voltage signal to a common line CL of the liquid crystal display panel 10.
The timing controller 6 supplies pixel data signals R, G, B Data inputted from an external source (not shown) to the data driver 2. Further, the timing controller 6 generates a gate control signal GDC and a data control signal DDC for respectively controlling the gate driver 4 and the data driver 2 in response to control signals inputted from the external source (not shown). The gate control signal GDC includes a gate start pulse, a gate shift clock signal and a gate output enable signal. The data control signal DDC includes a source start pulse, a source shift clock signal, a source output enable signal and a polarity control signal.
In addition, the gate driver 4 sequentially supplies a scan pulse to the gate lines GL1 . . . GLn in response to the gate control signal GDC from the timing controller 6. Accordingly, the gate driver 4 drives a thin film transistor TFT, which is connected to one of the gate lines GL1 . . . GLn. Further, the data driver 2 supplies pixel voltage signals of one horizontal line to the data lines DL1 . . . DLm for each horizontal period in response to the data control signal DDC. Particularly, the data driver 2 converts the digital pixel signal data R, G, B Data into analog pixel voltage signals using a gamma voltage from a gamma voltage generator (not shown) and supplies the converted analog pixel voltage signals. Moreover, the common voltage generator 8 generates a common voltage and supplies the generated common voltage to a common electrode, which forms a horizontal electric field with a pixel electrode, through the common line CL.
The liquid crystal display panel 10 includes a thin film transistor TFT formed at each of intersections of the gate lines GL1 . . . GLn and the data lines DL1 . . . DLm, and a liquid crystal cell connected to each thin film transistor TFT. The thin film transistors TFTs and the liquid crystal cells are arranged in a matrix shape. The thin film transistors TFT supply the data from the data lines DL1 . . . DLm to the liquid crystal cells in response to the gate signal from the gate line GL1 . . . GLn. The liquid crystal cell is made of the pixel electrode which is connected to the thin film transistor TFT, and a common electrode which forms a horizontal electric field with and in parallel to the pixel electrode and is connected to the common line CL, thus it can be equivalently indicated as a liquid crystal capacitor Clc. The liquid crystal cell Clc includes a storage capacitor Cst formed of the common line CL and the pixel electrode which overlap each other with an insulating film of at least one layer therebetween in order to maintain the pixel voltage signal charged in the liquid crystal capacitor Clc until the next pixel voltage signal is charged therein.
Accordingly, the horizontal electric field type liquid crystal display device can improve the picture quality when it is driven using a dot inversion method. However, there is a problem in that its power consumption is high.